Many government and public entities have landfill sites that need to be remediated. The solution for many of these sites is in-place containment using low permeability layers, barriers, or capillary barriers to control water transport of contaminants. The term “cap” is used hereinafter to describe any of these types of barriers. With this approach, it will be necessary to institute long term monitoring systems to ensure cap performance. System requirements include low maintenance, long lifespan, and economical implementation.
Often, monitoring at closed waste sites is needed for, e.g., 30 years without consideration of additional monitoring. At present, a water moisture monitoring strategy might involve multiple embedded sensors, each wired to a data logger or telemetry unit. The wires present obstacles to heavy equipment at the time of cap (barrier) construction, and subsequent cap maintenance. Use of wired sensors also implies cap penetrations. Any maintenance of sensors requires additional penetrations through the cap.
Monitoring of various parameters is also useful in a variety of other applications. For example, structural integrity of a bridge degrades with time due to environmental conditions. Exposure of bridge structures to harmful materials such as salts promotes oxidation of steel components of such structures. Such oxidation may be due to direct exposure of a bridge structure to harmful material such as chlorides in the salts or it may be due to slow infiltration of chlorides into reinforced concrete sections. Chlorides can corrode the reinforcing steel rebar in concrete bridge decks, requiring regular maintenance to ensure the health and safety of bridges. Although the diffusion rate of chlorides may be slow, the resulting corrosion can expand the volume of reinforcing bars (rebars) of the structure and cause the surrounding concrete to crack. Unless preventive maintenance is performed regularly, bridge life spans can be significantly shortened. Detection of corroding rebar in concrete may be difficult, and efforts to remedy such corrosion may be difficult without performing extensive rebuilding of the structure.
Acquiring knowledge as to when and where to perform such maintenance has typically been a costly and time-consuming process. Current methods for analyzing the levels of chlorides in bridge decks involve extracting concrete core samples and analyzing them in a laboratory setting, which is laborious and time consuming. Many tests are required, since it typically takes several years for critical chloride concentration levels to be reached. During bridge inspection, lanes are typically closed, and the bridge is usually sampled only at a few points along the deck. Accordingly, monitoring costs to identify deterioration of bridge structures can be significant.
Thus, it is desirable to develop improved sensor technologies to overcome the above-noted problems.